The present invention relates to continuous caster molds having an opposed pair of broad walls and an opposed pair of adjustably spaced narrow walls and more particularly to such a continuous caster mold having heated end walls for minimizing edge gap.
In the continuous casting of steel, it is known to utilize molds having a pair of opposed broad walls and a pair of opposed narrow walls in which at least one of the narrow walls is adjustable for changing the width of the slab during the actual casting operation. Normally, the thickness of the slab being cast on currently existing casters is within the range of 6-10 inches (15-25 cm). For slabs of this thickness, the mold walls are essentially rectangular so that the opening or cavity in the mold has straight sides. Molten metal is introduced into the mold from a tundish or ladle through a refractory pouring tube. The level of molten metal within the mold is maintained at a predetermined level below the top of the mold, generally on the order of 4-5 inches (10-13 cm).
The broad and narrow walls are generally made of a relatively thin copper or copper alloy plate attached to a relatively thick steel backup plate for support. The walls are cooled by the flow of water through channels in the back of the copper plates and in the backup plates. The molten metal in contact with the water cooled walls solidifies, permitting a partially solidified slab to be drawn out of the bottom of the mold as molten metal is introduced into the top of the mold.
The molten metal is on the order of 2800.degree.-2900.degree. F. (1540.degree.-1590.degree. C.). The hottest portion of the mold is the portion immediately beneath the surface or meniscus of the molten metal. The contact between the molten metal and the end wall at the meniscus heats the surface of the end wall and causes the end wall to expand.
However, immediately above the meniscus, no molten metal is in contact with the end wall but cooling water is in contact with the rear surface of the end wall. Therefore, an extreme temperature differential exists in the end wall between the portion of each end wall immediately below the meniscus and that immediately above the meniscus. The cooler metal above the meniscus expands only a fraction as much as the hot portion of the end wall in contact with the molten metal. The expansion of the end wall just beneath the meniscus urges the broad walls slightly farther apart in this area. Since the side walls are rigid and the upper portion of the end wall does not expand with the portion of the end wall beneath the surface of the molten metal, a gap forms between the upper portion of the end wall and the broad walls. While this gap is not initially serious, flux, molten metal and other contaminants can enter the gap. Continued service or prolonged casting can lead to a buildup of contaminants which will widen the gap. Width changes to the mold, during which the end walls are moved with respect to the casting direction, can also lead to buildup of contaminants and widening of the gap. Combination of the factors contributing to buildup of the contaminants can eventually cause breakouts or early stoppage of casting.
What is needed is a method and apparatus for equalizing the temperature of the end wall above the level of molten metal in the mold with that below the surface of the molten metal to prevent edge gap related casting problems.